Hi Maritza,
the Moodle App allows having several accounts in the same device, but each user will have to re-enter his account when he starts using the app.
We recommend you to go to "Site administration > Mobile app > Mobile features" and enable "Force log out", otherwise students will be able to enter any account stored in that device without entering the password and that's a security issue.
Students will need to enter the password when they want to re-enter their account, but the app will keep all the data they have previously downloaded.
Cheers,
Dani